Generally, a vacuum transfer system includes a vacuum pump that is operated by compressed air supplied thereto at a high speed, and a gripper from which air is expelled by the vacuum pump. Here, the vacuum transfer system is configured such that, when a negative pressure is produced in the vacuum pump and in the gripper, which holds an object to be transferred, the object can be transferred to a predetermined desired location by a robot unit.
In the vacuum transfer system, it is required to control the supply of the compressed air, and the present invention relates to a valve that executes the control of the supply of the compressed air.
A typical air control valve used in the vacuum transfer system is configured such that an outlet of the air control valve can be opened or closed by a piston that reciprocates in response to an on/off operation of an electronic control valve that is used to operate the air control valve. In other words, part of the compressed air that has been supplied into a valve casing through an inlet passes through the electronic control valve, and pressurizes the piston placed inside a piston chamber. Here, when the electronic control valve is in a turned on state, the electronic control valve moves the piston rearward and opens the outlet. However, when the electronic control valve is in a turned off state, the electronic control valve moves the piston forward and closes the outlet.
Although the air control valve having the above-mentioned construction is typically used in the vacuum transfer system, the related art air control valve is problematic as follows.
First, the above-mentioned valve construction that is configured to operate both the electronic control valve and the air control valve so as to realize the control of the supply of compressed air is not suitable for simple and repeated transfer work. That is, this valve construction should frequently repeat the on/off operation, so the valve construction consumes an excessive amount of electricity, reduces the expected life span of elements, and may cause malfunction. When the turned on state of the valve is continued in an effort to solve the problems, it is almost impossible to efficiently execute transfer work, and an excessive amount of energy may be wasted.
Second, the air control valve is configured to be operated by the on/off operation of the electronic control valve. Therefore, when the electronic control valve, as an example, fails to be operated normally, the air control valve may not control the operation of the vacuum transfer system.
Third, in the vacuum transfer system, it is practically required to determine the supply of compressed air or the stopping of the supply of the compressed air using the level of vacuum pressure formed in the vacuum pump or in an air exhaust chamber. In other words, the air control valve should be configured to be closed when the level of vacuum pressure reaches a predetermined sufficient level. However, the air control valve having the above-mentioned construction is operated in response to an electric signal, so the operational precision of the air control valve is reduced.